The Aral Sea Basin in Central Asia is an important geographical environment unit in the center of Eurasia. It is of great significance to the ecological protection and sustainable development of Central Asia to carry out dynamic monitoring and effective evaluation of the eco-environmental quality of the Aral Sea Basin. In this study, the arid remote sensing ecological index (ARSEI) for large-scale arid areas was developed, which coupled the information of the greenness index, the salinity index, the humidity index, the heat index, and the land degradation index of arid areas. The ARSEI was used to monitor and evaluate the eco-environmental quality of the Aral Sea Basin from 2000 to 2019. The results show that the greenness index, the humidity index and the land degradation index had a positive impact on the quality of the ecological environment in the Aral Sea Basin, while the salinity index and the heat index exerted a negative impact on the quality of the ecological environment. The eco-environmental quality of the Aral Sea Basin demonstrated a trend of initial improvement, followed by deterioration, and finally further improvement. The spatial variation of these changes was significant. From 2000 to 2019, grassland and wasteland (saline alkali land and sandy land) in the central and western parts of the basin had the worst ecological environment quality. The areas with poor ecological environment quality are mainly distributed in rivers, wetlands, and cultivated land around lakes. During the period from 2000 to 2019, except for the surrounding areas of the Aral Sea, the ecological environment quality in other areas of the Aral Sea Basin has been improved in general. The correlation coefficients between the change in the eco-environmental quality and the heat index and between the change in the eco-environmental quality and the humidity index were -0.593 and 0.524, respectively. Climate conditions and human activities have led to different combinations of heat and humidity changes in the eco-environmental quality of the Aral Sea Basin. However, human activities had a greater impact. The ARSEI can quantitatively and intuitively reflect the scale and causes of large-scale and long-time period changes of the eco-environmental quality in arid areas; it is very suitable for the study of the eco-environmental quality in arid areas.

Frequent periods of drought conditions are known to limit plant performance, primary production, and ecosystem stability in arid and semi-arid desert steppe environments. Plants often avoid competition by shifting their water use seasonally, which affects the water-use patterns of dominant species as well as the composition and structure of plant communities. However, the water-use strategies of dominant herbaceous species, which grow under natural field conditions in the desert steppe region of Ningxia Hui Autonomous Region, China, are poorly known. Here, we explored the possible sources of water uptake and water-use efficiency (WUE) of three dominant herbaceous plant species (Stipa breviflora, Agropyron mongolicum, and Glycyrrhiza uralensis) in a native desert steppe in the semi-arid area of Ningxia through an analysis of multiple parameters, including (1) the stable isotopic oxygen and hydrogen (δ ¹⁸O and δ ²H) compositions of precipitation, soil water, and stem water, (2) the carbon isotope ( ¹³C) composition of leaves, and (3) the soil water contents, based on field sampling across varying water conditions from June to September, 2017. Frequent small precipitation events replenished shallow soil water, whereas large events only percolated down to the deep soil layers. Changes in soil water availability affected the water-use patterns of plants. Generally, during light precipitation periods, the deep root system of G. uralensis accessed deeper (>80 cm) soil water, whereas S. breviflora and A. mongolicum, which only have shallow roots, primarily absorbed water from the shallow and middle soil layers. As precipitation increased, all three plant species primarily obtained water from the shallow soil layers. Variation in soil water uptake between the dry and wet seasons enabled plants to make better use of existing satoil water. In addition, the δ ¹³C values of G. uralensis and S. breviflora were higher than those of A. mongolicum. The δ ¹³C values of the three plant species were significantly negatively correlated with soil water content. Therefore, G. uralensis and S. breviflora maintained a higher WUE through their conservative and water-saving strategies across the entire growing season. In contrast, A. mongolicum, with a relatively low WUE in the wet season but a high WUE in the dry season, exhibited a more flexible water-use strategy. The different water-use strategies of these dominant plant species demonstrated the mechanisms by which plant communities can respond to drought.

High water consumption and inefficient irrigation management in the agriculture sector of the middle and lower reaches of the Amu Darya River Basin (ADRB) have significantly influenced the gradual shrinking of the Aral Sea and its ecosystem. In this study, we investigated the crop water consumption in the growing seasons and the irrigation water requirement for different crop types in the lower ADRB during 2004-2017. We applied the FAO Penman-Monteith method to estimate reference evapotranspiration (ET₀) based on daily climatic data collected from four meteorological stations. Crop evapotranspiration (ET_c) of specific crop types was calculated by the crop coefficient. Then, we analyzed the net irrigation requirement (NIR) based on the effective precipitation with crop water requirements. The results indicated that the lowest monthly ET₀ values in the lower ADRB were found in December (18.2 mm) and January (16.0 mm), and the highest monthly ET₀ values were found in June and July, with similar values of 211.6 mm. The annual ET_c reached to 887.2, 1002.1, and 492.0 mm for cotton, rice, and wheat, respectively. The average regional NIR ranged from 514.9 to 715.0 mm in the 10 Irrigation System Management Organizations (UISs) in the study area, while the total required irrigation volume for the whole region ranged from 4.2×10⁹ to 11.6×10⁹ m³ during 2004-2017. The percentages of NIR in SIW (surface irrigation water) ranged from 46.4% to 65.2% during the study period, with the exceptions of the drought years of 2008 and 2011, in which there was a significantly less runoff in the Amu Darya River. This study provides an overview for local water authorities to achieve optimal regional water allocation in the study area.

Groundwater forms the main freshwater supply in arid and semi-arid areas, and contamination of this precious resource is complicated by the slow rate of recharge in these areas. Nitrate contamination of groundwater is a global water quality problem, as it entails threat to human health as well as aquatic ecosystems. Source identification of contamination is the cornerstone and a prerequisite for any effective management program of water quality. Stable isotope composition of the dissolved nitrate (δ¹⁵N-NO₃^- and δ ¹⁸O-NO₃^-) has been applied to identify NO₃^- sources and the main transformation processes in the upper aquifer system (A1/2, A4, and B2/A7 aquifers) in the Wadi Shueib catchment area, Jordan. Moreover, the stable isotope compositions of the groundwater (δ²H-H₂O and δ1⁸O-H₂O) in conjunction with the groundwater hydrochemistry were integrated to investigate the origin and evolution of the groundwater. Results revealed that groundwater in the study area is fresh and hard-very hard water, and mainly a Ca-Mg-Cl type. NO₃^- concentration was in the range of 7.0-74.0 mg/L with an average of 37.0 mg/L. Most of the samples showed concentration higher than the natural background concentration of NO₃^- (5.0-10.0 mg/L). The δ ²H-H₂O and δ¹⁸O-H₂O values indicated that the groundwater is meteoric, and of Mediterranean origin, with a strong evaporation effect. The δ¹⁵N-NO₃^- values ranged between 6.0‰ and 11.3‰ with an average of 8.7‰, and the δ¹⁸O-NO₃^- values ranged between 1.6‰ and 5.9‰ with an average of 3.4‰. These values are in conformity with the stable isotope composition of nitrate derived the nitrification of wastewater/manure, and soil NH₄. Nitrification and denitrification are the main transformation processes affecting nitrogen species. Statistical analysis revealed no significant differences in the δ²H-H₂O and δ¹⁸O-H₂O values, and δ¹⁵N-NO₃^- and δ ¹⁸O-NO₃^- values for the three aquifers (A1/2, A4, and B2/A7), indicating that the groundwater of these aquifers has the same origin, and a common source of pollution.

In this study, we analyzed the hydrological and meteorological data from the Syr Darya River Basin during the period of 1930-2015 to investigate variations in river runoff and the impacts of climate change and human activities on river runoff. The Syr Darya River, which is supplied by snow and glacier meltwater upstream, is an important freshwater source for Central Asia, as nearly half of the population is concentrated in this area. River runoff in this arid region is sensitive to climate change and human activities. Therefore, estimation of the climatic and hydrological changes and the quantification of the impacts of climate change and human activities on river runoff are of great concern and important for regional water resources management. The long-term trends of hydrological time series from the selected 11 hydrological stations in the Syr Darya River Basin were examined by non-parametric methods, including the Pettitt change point test and Mann-Kendall trend tests. It was found that 8 out of 11 hydrological stations showed significant downward trends in river runoff. Change of river runoff variations occurred in the year around 1960. Moreover, during the study period (1930-2015), annual mean temperature, annual precipitation, and annual potential evapotranspiration in the river basin increased substantially. We employed hydrological sensitivity method to evaluate the impacts of climate change and human activities on river runoff based on precipitation and potential evapotranspiration. It was estimated that human activities accounted for over 82.6%-98.7% of the reduction in river runoff, mainly owing to water withdrawal for irrigation purpose. The observed variations in river runoff can subsequently lead to adverse ecological consequences from an ecological and regional water resources management perspective.

The southwestern Iran is one of the regions that are most prone to dust events. The objective of this study is the analysis of the spatial and temporal distributions of dust deposition rate as a key factor for finding the relative impact of the dust. First, the monthly mean aerosol optical thickness (AOT) from Moderate Resolution Imaging Spectroradiometer (MODIS) was analyzed and compared with the dust amount variations from ground deposition rate (GDR), and the results were further used to investigate the spatial and temporal distributions of dust events in southwestern Iran for the period between 2014 and 2015. Moving air mass trajectories, using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, were proven to be a discriminator of their local and regional origin. The results from GDR analysis produced a correlation coefficient between dust event history and deposition rates at dust magnitudes of >0.93 that is meaningful at the 95% confidence level. Furthermore, the deposition rates varied from 3 g/m² per month in summer to 10 g/m² per month in spring and gave insight into the transport direction of the dust. Within the same time series, AOT correspondences with MODIS on Terra in four aerosol thickness layers (clean, thin, thick, and strong thick) were shown in relation to each other. The deepest mixed layers were observed in spring and summer with a thickness of approximately 3500 m above ground level in the study area. Investigations of ground-based observations were correlated with the same variations for each aerosol thickness layer from MODIS images and they can be applied to discriminate layers of aeolian dust from layers of other aerosols. Together, dust distribution plots from AOT participated to enhance mass calculations and estimation deposition rates from the thick and strong thick aerosol thickness layers using the results from GDR. Despite all the advances of AOT, under certain circumstances, ground-based observations are better able to represent aerosol conditions over the study area, which were tested in southwestern Iran, even though the low number of observations is a commonly acknowledged drawback of GDR.

Drought was a severe recurring phenomenon in Iraq over the past two decades due to climate change despite the fact that Iraq has been one of the most water-rich countries in the Middle East in the past. The Iraqi Kurdistan Region (IKR) is located in the north of Iraq, which has also suffered from extreme drought. In this study, the drought severity status in Sulaimaniyah Province, one of four provinces of the IKR, was investigated for the years from 1998 to 2017. Thus, Landsat time series dataset, including 40 images, were downloaded and used in this study. The Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI) were utilized as spectral-based drought indices and the Standardized Precipitation Index (SPI) was employed as a meteorological-based drought index, to assess the drought severity and analyse the changes of vegetative cover and water bodies. The study area experienced precipitation deficiency and severe drought in 1999, 2000, 2008, 2009, and 2012. Study findings also revealed a drop in the vegetative cover by 33.3% in the year 2000. Furthermore, the most significant shrinkage in water bodies was observed in the Lake Darbandikhan (LDK), which lost 40.5% of its total surface area in 2009. The statistical analyses revealed that precipitation was significantly positively correlated with the SPI and the surface area of the LDK (correlation coefficients of 0.92 and 0.72, respectively). The relationship between SPI and NDVI-based vegetation cover was positive but not significant. Low precipitation did not always correspond to vegetative drought; the delay of the effect of precipitation on NDVI was one year.

Central Asia is located in the hinterland of Eurasia, comprising Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, and Tajikistan; over 93.00% of the total area is dryland. Temperature rise and human activities have severe impacts on the fragile ecosystems. Since the 1970s, nearly half the great lakes in Central Asia have shrunk and rivers are drying rapidly owing to climate changes and human activities. Water shortage and ecological crisis have attracted extensive international attention. In general, ecosystem services in Central Asia are declining, particularly with respect to biodiversity, water, and soil conservation. Furthermore, the annual average temperature and annual precipitation in Central Asia increased by 0.30°C/decade and 6.9 mm/decade in recent decades, respectively. Temperature rise significantly affected glacier retreat in the Tianshan Mountains and Pamir Mountains, which may intensify water shortage in the 21^st century. The increase in precipitation cannot counterbalance the aggravation of water shortage caused by the temperature rise and human activities in Central Asia. The population of Central Asia is growing gradually, and its economy is increasing steadily. Moreover, the agricultural land has not been expended in the last two decades. Thus, water and ecological crises, such as the Aral Sea shrinkage in the 21^st century, cannot be attributed to agriculture extension any longer. Unbalanced regional development and water interception/transfer have led to the irrational exploitation of water resources in some watersheds, inducing downstream water shortage and ecological degradation. In addition, accelerated industrialization and urbanization have intensified this process. Therefore, all Central Asian countries must urgently reach a consensus and adopt common measures for water and ecological protection.

Desertification is one of the most serious environmental problems in the world, especially in the arid desert regions. Combating desertification, therefore, is an urgent task on a regional or even global scale. The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the ''Dead Sea'' due to few organisms can exist in such a harsh environment. The Taklimakan Desert Highway, the longest desert highway (a total length of 446 km) across the mobile desert in the world, was built in the 1990s within the Taklimakan Desert. It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang, China. However, wind-blow sand seriously damages the smoothness of the desert highway and, in this case, mechanical sand control system (including sand barrier fences and straw checkerboards) was used early in the life of the desert highway to protect the road. Unfortunately, more than 70% of the sand barrier fences and straw checkerboards have lost their functions, and the desert highway has often been buried and frequently blocked since 1999. To solve this problem, a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000. However, some potential problems still exist for the sustainable development of the desert highway, such as water shortage, strong sandstorms, extreme environmental characteristics and large maintenance costs. The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway. Ultimately, we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway, such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater, screening halophytes to restore vegetation in the case of soil salinization, and planting cash crops, such as Cistanche, Wolfberry, Apocynum and other cash crops to decrease the high cost of maintenance on highways and shelterbelts.

The rapid economic development that the Hotan Oasis in Xinjiang Uygur Autonomous Region, China has undergone in recent years may face some challenges in its ecological environment. Therefore, an analysis of the spatiotemporal changes in ecological environment of the Hotan Oasis is important for its sustainable development. First, we constructed an improved remote sensing-based ecological index (RSEI) in 1990, 1995, 2000, 2005, 2010, 2015 and 2020 on the Google Earth Engine (GEE) platform and implemented change detection for their spatial distribution. Second, we performed a spatial autocorrelation analysis on RSEI distribution map and used land-use and land-cover change (LUCC) data to analyze the reasons of RSEI changes. Finally, we investigated the applicability of improved RSEI to arid area. The results showed that mean of RSEI rose from 0.41 to 0.50, showing a slight upward trend. During the 30-a period, 2.66% of the regions improved significantly, 10.74% improved moderately and 32.21% improved slightly, respectively. The global Moran's I were 0.891, 0.889, 0.847 and 0.777 for 1990, 2000, 2010 and 2020, respectively, and the local indicators of spatial autocorrelation (LISA) distribution map showed that the high-high cluster was mainly distributed in the central part of the Hotan Oasis, and the low-low cluster was mainly distributed in the outer edge of the oasis. RSEI at the periphery of the oasis changes from low to high with time, with the fragmentation of RSEI distribution within the oasis increasing. Its distribution and changes are predominantly driven by anthropologic factors, including the expansion of artificial oasis into the desert, the replacement of desert ecosystems by farmland ecosystems, and the increase in the distribution of impervious surfaces. The improved RSEI can reflect the eco-environmental quality effectively of the oasis in arid area with relatively high applicability. The high efficiency exhibited with this approach makes it convenient for rapid, high frequency and macroscopic monitoring of eco-environmental quality in study area.

The gradual shrinkage of the Aral Sea has led to not only the degradation of the unique environments of the Aral Sea, but also numerous and fast developing succession processes in the neighborhood habitats surrounding the sea. In this study, we investigated the vegetative succession processes related to the Aral Sea shrinkage in the Eastern Cliff of the Ustyurt Plateau in Republic of Uzbekistan, Central Asia. We compared the results of our current investigation (2010-2017) on vegetative communities with the geobotany data collected during the 1970s (1970-1980). The results showed great changes in the mesophytic plant communities and habitat aridization as a result of the drop in the underground water level, which decreased atmospheric humidity and increased the salt content of the soil caused by the shrinkage of the Aral Sea. In the vegetative communities, we observed a decrease in the Margalef index (D_Mg), which had a positive correlation with the poly-dominance index (I-D). The main indications of the plant communities' transformation were the loss of the weak species, the appearance of new communities with low species diversity, the stabilization of the projective cover of former resistant communities, as well as the appearance of a new competitive species, which occupy new habitats.

Zarrineh River is located in the northwest of Iran, providing more than 40% of the total inflow into the Lake Urmia that is one of the largest saltwater lakes on the earth. Lake Urmia is a highly endangered ecosystem on the brink of desiccation. This paper studied the impacts of climate change on the streamflow of Zarrineh River. The streamflow was simulated and projected for the period 1992-2050 through seven CMIP5 (coupled model intercomparison project phase 5) data series (namely, BCC-CSM1-1, BNU-ESM, CSIRO-Mk3-6-0, GFDL-ESM2G, IPSL-CM5A-LR, MIROC-ESM and MIROC-ESM-CHEM) under RCP2.6 (RCP, representative concentration pathways) and RCP8.5. The model data series were statistically downscaled and bias corrected using an artificial neural network (ANN) technique and a Gamma based quantile mapping bias correction method. The best model (CSIRO-Mk3-6-0) was chosen by the TOPSIS (technique for order of preference by similarity to ideal solution) method from seven CMIP5 models based on statistical indices. For simulation of streamflow, a rainfall-runoff model, the hydrologiska byrans vattenavdelning (HBV-Light) model, was utilized. Results on hydro-climatological changes in Zarrineh River basin showed that the mean daily precipitation is expected to decrease from 0.94 and 0.96 mm in 2015 to 0.65 and 0.68 mm in 2050 under RCP2.6 and RCP8.5, respectively. In the case of temperature, the numbers change from 12.33°C and 12.37°C in 2015 to 14.28°C and 14.32°C in 2050. Corresponding to these climate scenarios, this study projected a decrease of the annual streamflow of Zarrineh River by half from 2015 to 2050 as the results of climatic changes will lead to a decrease in the annual streamflow of Zarrineh River from 59.49 m³/s in 2015 to 22.61 and 23.19 m³/s in 2050. The finding is of important meaning for water resources planning purposes, management programs and strategies of the Lake's endangered ecosystem.

This study aimed to elucidate the influence of inflow water on the salinity concentration process of a saline lake and the mass balance of Lake Issyk-Kul, a tectonic saltwater lake in Kyrgyzstan. Based on the survey results and meteorological data from 2012 to 2015, we analyzed the dissolved chemical composition loads due to water inflow. Then, we discussed the relationship between the increase in salinity and water inflow into the lake. Through the water quality analysis data, we used the tank model to estimate the river inflow and analyze the loads by the L-Q curve. The groundwater loads were then estimated from the average annual increase in salinity of the lake over a period of 30 a. The results suggest that Lake Issyk-Kul was temporarily freshened between about AD 1500 and 1800 when an outflowing river existed, and thereafter, it became a closed lake in AD 1800 and continued to remain a saline lake until present. The chemical components that cause salinization are supplied from the rivers and groundwater in the catchment area, and when they flow into the lake, Ca²⁺, HCO₃^- and Mg²⁺ precipitate as CaCO₃ and MgCO₃. These compounds were confirmed to have been left on the lakeshore as evaporite. The model analysis showed that 1.67 mg/L of Ca²⁺ and Mg²⁺ supplied from rivers and groundwater are precipitated as evaporite and in other forms per year. On the other hand, salinity continues to remain in the lake water at a rate of 27.5 mg/L per year. These are the main causes of increased salinity in Lake Issyk-Kul. Since Na⁺ and Cl^- are considered to be derived from geothermal water, they will continue to flow in regardless of the effects of human activities. Therefore, as long as these components are accumulated in Lake Issyk-Kul as a closed lake, the salinity will continue to increase in the future.

Dust storms in arid and desert areas affect radiation budget, air quality, visibility, enzymatic activities, agricultural products and human health. Due to increased drought and land use changes in recent years, the frequency of dust storms occurrence in Iran has been increased. This study aims to identify dust source areas in the Sistan watershed (Iran-Afghanistan borders)-an important regional source for dust storms in southwestern Asia, using remote sensing (RS) and bivariate statistical models. Furthermore, this study determines the relative importance of factors controlling dust emissions using frequency ratio (FR) and weights of evidence (WOE) models and interpretability of predictive models using game theory. For this purpose, we identified 211 dust sources in the study area and generated a dust source distribution map-inventory map-by dust source potential index based on RS data. In addition, spatial maps of topographic factors affecting dust source areas including soil, lithology, slope, Normalized difference vegetation index (NDVI), geomorphology and land use were prepared. The performance of two models (WOE and FR) was evaluated using the area under curve (AUC) of the receiver operating characteristic curve. The results showed that soil, geomorphology and slope exhibited the greatest influence in the dust source areas. The 55.3% (according to FR) and 62.6% (according to WOE) of the total area were classified as high and very high potential dust sources, while both models displayed acceptable accuracy with subsurface levels of 0.704 for FR and 0.751 for WOE, although they predict different fractions of dust potential classes. Based on Shapley additive explanations (SHAP), three factors, i.e., soil, slope and NDVI have the highest impact on the model's output. Overall, combination of statistic-based predictive models (or data mining models), RS and game theory techniques can provide accurate maps of dust source areas in arid and semi-arid regions, which can be helpful for mitigation of negative effects of dust storms.

Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline areas. The aim of this study was to assess the spatial variability of various vegetation communities in relation to edaphic factors in the Great Salt Desert, central Iran. Fifteen vegetation communities were identified using the physiognomy-floristic method. Coverage and density of vegetation communities were determined using the transect plot method. Forty soil samples were collected from major horizons of fifteen profiles in vegetation communities, and analyzed in terms of following soil physical and chemical characteristics: soil texture, soluble Na ⁺ concentration, sodium adsorption ratio (SAR), electrical conductivity (EC), pH, organic matter content, soluble Mg ²⁺ and Ca ²⁺ concentrations, carbonate and gypsum contents, and spontaneously- and mechanically-dispersible clay contents. Redundancy analysis was used to investigate the relationships between vegetation dynamic and edaphic factors. The generalized linear method (GLM) was used to find the plant species response curves against edaphic factors. Results showed that plant species responded differently to edaphic factors, in which soluble sodium concentration, EC, SAR, gypsum content and soil texture were identified as the most discriminative edaphic factors. The studied plant species were also found to have different ecological requirements and tolerance to edaphic factors, in which Tamarix aphylla and Halocnemum strobilaceum were identified as the most salt-resistant species in the region. Furthermore, the presence of Artemisia sieberi was highly related to soil sand and gypsum contents. The results implied that exploring the plant species response curves against edaphic factors can assist managers to lay out more appropriate restoration plans in similar arid areas.

Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security. However, this ecosystem is potentially vulnerable to climate change (e.g., precipitation) and human activity (e.g., grazing). Despite this, the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored. Therefore, we conducted a systematic field investigation and a clipping experiment (simulating different intensities of grazing) in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass (AGB), soil volumetric water content (SVWC), and precipitation use efficiency (PUE) during the period of 2014-2017. We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer, respectively. We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation, and that PUE may be relatively low in years with either low or excessive precipitation. The PUE values were generally higher in the rapid growing season (April-July) than in the entire growing season (April-October). Overall, moderate grazing can promote plant growth under water stress conditions. The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season (April-July), but it was lower in the clipped plots than in the unclipped plots in the slow growing season (August-October). Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.

Qinghai Lake is the largest saline lake in China. The change in the lake volume is an indicator of the variation in water resources and their response to climate change on the Qinghai-Tibetan Plateau (QTP) in China. The present study quantitatively evaluated the effects of climate change and land use/cover change (LUCC) on the lake volume of the Qinghai Lake in China from 1958 to 2018, which is crucial for water resources management in the Qinghai Lake Basin. To explore the effects of climate change and LUCC on the Qinghai Lake volume, we analyzed the lake level observation data and multi-period land use/land cover (LULC) data by using an improved lake volume estimation method and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model. Our results showed that the lake level decreased at the rate of 0.08 m/a from 1958 to 2004 and increased at the rate of 0.16 m/a from 2004 to 2018. The lake volume decreased by 105.40×10⁸ m³ from 1958 to 2004, with the rate of 2.24×10⁸ m³/a, whereas it increased by 74.02×10⁸ m³ from 2004 to 2018, with the rate of 4.66×10⁸ m³/a. Further, the climate of the Qinghai Lake Basin changed from warm-dry to warm-humid. From 1958 to 2018, the increase in precipitation and the decrease in evaporation controlled the change of the lake volume, which were the main climatic factors affecting the lake volume change. From 1977 to 2018, the measured water yield showed an "increase-decrease-increase" fluctuation in the Qinghai Lake Basin. The effects of climate change and LUCC on the measured water yield were obviously different. From 1977 to 2018, the contribution rate of LUCC was -0.76% and that of climate change was 100.76%; the corresponding rates were 8.57% and 91.43% from 1977 to 2004, respectively, and -4.25% and 104.25% from 2004 to 2018, respectively. Quantitative analysis of the effects and contribution rates of climate change and LUCC on the Qinghai Lake volume revealed the scientific significance of climate change and LUCC, as well as their individual and combined effects in the Qinghai Lake Basin and on the QTP. This study can contribute to the water resources management and regional sustainable development of the Qinghai Lake Basin.

Crop residue is a major source of soil organic matter; therefore, application of crop straw to soil contributes to the sustainable development of organic agriculture. To better understand the transformation of crop straw in orchard soils, we investigated the relationship between the characteristics of straw decomposition and functional diversity of associated microbial communities in a long-term peach orchard, China. Mesh bags, each containing 30 g of corn or bean straw, were buried at a soil depth of 20 cm in a 12-year-old peach orchard for 360 d (October 2011-October 2012). Three treatments were applied, i.e., fresh corn straw, fresh corn straw with nitrogen fertilizer (urea, 10.34 g/kg), and fresh bean straw. Changes in straw residual rate, straw water content and soil conditions were monitored after treatment. The functional diversity of straw-associated microbial communities was analyzed by the Biolog-Eco microplate assay. During the decomposition process, straw residual rates did not vary considerably from 10 d (30.4%-45.4%) to 360 d (19.0%-30.3%). Irrespective of nitrogen addition, corn straw decomposed faster than bean straw. Corn straw with nitrogen fertilizer yielded the highest average well color development (AWCD) values (1.11-1.67), followed by corn straw (1.14-1.68) and bean straw (1.18-1.62). Although the AWCD values did not differ significantly among the three treatments, substantial differences occurred across various time periods of the decomposition process (P<0.01). In terms of carbon source utilization, the dominant microbial groups fed mainly on saccharides. Hard-to-decompose substances gradually accumulated in the middle and late stages of straw decomposition. Of the six categories of carbon sources tested, the utilization rate of aromatics was the lowest with corn straw, whereas that of polymers was the lowest with bean straw. Among different treatments, straw residual rate was negatively correlated to soil available phosphorous, soil available potassium and soil temperature (P<0.05), but not to soil water content. In some cases (corn straw with or without nitrogen fertilizer), straw residual rate was negatively correlated to straw water content, amino acid utilization and carboxylic acid utilization, and positively correlated with microbial species richness and evenness (P<0.05). Microbial community associated with corn and bean straw decomposition in soil was respectively dominated by aromatic- and polymer-metabolizing groups during the middle and late stages of this process, which could reduce the stability of microbial community structure and decrease the rate of straw decomposition in the fruit tree orchard.

The relationships between different aspects of diversity (taxonomic, structural and functional) and the aboveground biomass (AGB) as a major component of global carbon balance have been studied extensively but rarely under the simultaneous influence of forest dieback and management. In this study, we investigate the relationships between taxonomic, functional and structural diversity of woody species (trees and shrubs) and AGB along a gradient of dieback intensity (low, moderate, high and no dieback as control) under two contrasted management conditions (protection by central government vs. traditional management by natives) in a semi-arid oak (Quercus brantii Lindl.) forest ecosystem. AGB was estimated and taxonomic diversity, community weighted average (CWM) and functional divergence indices were produced. We found that the aerial biomass was significantly higher in the intensively used area (14.57 (±1.60) t/hm²) than in the protected area (8.70 (±1.05) t/hm²) due to persistence of some large trees but with decreasing values along the dieback intensity gradient in both areas. CWM of height (H), leaf nitrogen content (LNC) and leaf dry matter content (LDMC) were also higher in the traditional managed area than in the protected area. In contrast, in the protected area, the woody species diversity was higher and the inter-specific competition was more intense, explaining a reduced H, biomass and LDMC. Contrary to the results of CWM, none of the functional diversity traits (FDvar) was affected by dieback intensity and only FDvar values of LNC, leaf phosphorus content (LPC) and LDMC were influenced by management. We also found significantly positive linear relationships of AGB with CWM and FDvar indices in the protected area, and with taxonomic and structural diversity indices in the traditional managed area. These results emphasize that along a dieback intensity gradient, the leaf functional traits are efficient predictors in estimating the AGB in protected forests, while taxonomic and structural indices provide better results in forests under a high human pressure. Finally, species identity of the dominant species (i.e., Brant's oak) proves to be the main driver of AGB, supporting the selection effect hypothesis.

Sediment transport of sand particles by wind is one of the main processes leading to desertification in arid regions, which severely impairs the ability of mankind to produce and live by drifting sand into settlements. Optimization designs of artificial facilities have lately attracted extensive interest for human settlement systems in deserts because of their acceptable protection effect, convenience of implementation, and low material cost. However, the complexity of a settlement system poses challenges concerning finding suitable materials, artificial facilities, and optimization designs for sand deposition protection. In an effort to overcome these challenges, we propose a settlement system built with brick, solar panel, and building arrays to meet the basic needs of human settlements in arid regions while preventing wind-sand disasters. The wind flow and movement characteristics of sand particles in the brick, panel, and building arrays were calculated using computational fluid dynamics and discrete phase model. The performance of three types of arrays in wind-sand flow in terms of decreasing the wind velocity and sand-particle invasion distance was evaluated. The results show that the wind velocity near the surface and the sand invasion distance were significantly decreased in the space between the brick arrays through properly selected vertical size and interspaces, indicating that the brick arrays have an impressive sand fixing and blocking performance; their effective protection distance was 3-4 m. The building arrays increased the near-surface wind velocity among buildings, resulting in less deposition of sand particles. The solar panel arrays were similar to the building arrays in most cases, but the deposition of sand particles on solar panels exerted a negative effect on energy utilization efficiency. Therefore, taking the optimal configuration of the settlement system into consideration, this study concludes that (1) brick arrays, which were proven effective in preventing sand particles, must be arranged in an upwind area; (2) solar panel arrays could accelerate the wind flow, so they are best to be arranged at the place where sand particles deposited easily; and (3) building arrays present a better arrangement in downwind areas.

Agriculture needs to produce more food to feed the growing population in the 21^st century. It makes the reference crop water requirement (WREQ) a major challenge especially in regions with limited water and high water demand. Iran, with large climatic variability, is experiencing a serious water crisis due to limited water resources and inefficient agriculture. In order to overcome the issue of uneven distribution of weather stations, gridded Climatic Research Unit (CRU) data was applied to analyze the changes in potential evapotranspiration (PET), effective precipitation (EFFPRE) and WREQ. Validation of data using in situ observation showed an acceptable performance of CRU in Iran. Changes in PET, EFFPRE and WREQ were analyzed in two 30-a periods 1957-1986 and 1987-2016. Comparing two periods showed an increase in PET and WREQ in regions extended from the southwest to northeast and a decrease in the southeast, more significant in summer and spring. However, EFFPRE decreased in the southeast, northeast, and northwest, especially in winter and spring. Analysis of annual trends revealed an upward trend in PET (14.32 mm/decade) and WREQ (25.50 mm/decade), but a downward trend in EFFPRE (-11.8 mm/decade) over the second period. Changes in PET, EFFPRE and WREQ in winter have the impact on the annual trend. Among climate variables, WREQ showed a significant correlation (r=0.59) with minimum temperature. The increase in WREQ and decrease in EFFPRE would exacerbate the agricultural water crisis in Iran. With all changes in PET and WREQ, immediate actions are needed to address the challenges in agriculture and adapt to the changing climate.

Understanding the spatiotemporal patterns of the forage-livestock balance is imperative for regionally arranging animal husbandry production while ensuring sustainable grassland-ecosystem service use. The Xilin Gol steppe is an important native grassland resource in Inner Mongolia Autonomous Region, China. This study aimed to elucidate the dynamics of the forage-livestock balance in the Xilin Gol steppe during the period 2000-2015. We evaluated the forage production and corresponding livestock carrying capacity (LCC) in the growing seasons of 2000-2015 using remote sensing data and field surveys. The spatiotemporal patterns of the forage-livestock balance were then assessed at regional, city (including city, county and banner), and village scales using statistical and household survey data. The results showed that both forage production and LCC decreased in the Xilin Gol steppe from east to west. During the period 2000-2015, the regional average forage production and corresponding LCC fluctuated without following a distinct trend, but were consistent with the variations in precipitation. The forage-livestock balance varied with time, space, and scale. At the regional scale, steppes were overgrazed in the early 2000s, but a forage-livestock balance or even grazing potential was achieved in other years. At the city scale, approximately half of the region exhibited a "forage-livestock balance" since 2000. However, about half of the region still experienced overgrazing, which mainly located in the southwest sandy zones. Such changes may have been affected by the variations in grassland quality, forage production, compensation payment, and so on. We suggest a location-specific management scheme for grazing constraints, ecological compensation payment, and industry development to aid in harmonizing animal husbandry and environmental restoration, while promoting sustainable development goals by 2030.

Ants (Formicidae, Hymenoptera) play an important role in seed bank, seedling establishment and plant composition of arid ecosystems. Thus, knowing plant-ant interaction provides useful information for managers to design restoration and conservation plans. In this study, the roles of desert harvester ants (Messor intermedius and Messor melancholicus) and scavenger ants (Cataglyphis nodus and Lepisiota semenovi) on plant communities were investigated in arid ecosystems of southeastern Iran. Two vegetation types were distinguished in the study area and the nest density of ant species was determined. Furthermore, plant composition and soil seed bank were estimated at different distances from the ant nests. Results showed that the density of M. intermedius and M. melancholicus nests was higher in dwarf shrub-shrub vegetation type and the density of C. nodus and L. semenovi nests was higher in dwarf shrub vegetation type. The harvester and scavenger ants had enhanced the seed bank to 55% and 70%, respectively. Therefore, the role of scavenger ants on the plant communities' seed bank was greater than that of harvester ants. Although the scavenger ants were more influential on the annuals and the invasive plant species, the radius impact of the harvester ants on the perennials was greater, i.e., a positive interaction existed between the perennial plants and the harvester ants. C. nodus and L. semenovi played an important role in enhancing the ecosystem's potential for restoration through establishment of pioneer species in early stage of succession. The activity of M. intermedius is crucial for the development and maintenance of climax plant communities in arid ecosystems through assisting the plant species' establishment in late stage of succession. It is essential to preserve the diversity of these key ant species for the maintenance and sustainability of shrubs in arid ecosystems.

As the largest inland river basin of China, the Tarim River Basin (TRB), known for its various natural resources and fragile environment, has an increased risk of ecological crisis due to the intensive exploitation and utilization of water and land resources. Since the Ecological Water Diversion Project (EWDP), which was implemented in 2001 to save endangered desert vegetation, there has been growing evidence of ecological improvement in local regions, but few studies have performed a comprehensive ecological vulnerability assessment of the whole TRB. This study established an evaluation framework integrating the analytic hierarchy process (AHP) and entropy method to estimate the ecological vulnerability of the TRB covering climatic, ecological, and socioeconomic indicators during 2000-2017. Based on the geographical detector model, the importance of ten driving factors on the spatial-temporal variations of ecological vulnerability was explored. The results showed that the ecosystem of the TRB was fragile, with more than half of the area (57.27%) dominated by very heavy and heavy grades of ecological vulnerability, and 28.40% of the area had potential and light grades of ecological vulnerability. The light grade of ecological vulnerability was distributed in the northern regions (Aksu River and Weigan River catchments) and western regions (Kashgar River and Yarkant River catchments), while the heavy grade was located in the southern regions (Kunlun Mountains and Qarqan River catchments) and the Mainstream catchment. The ecosystems in the western and northern regions were less vulnerable than those in the southern and eastern regions. From 2000 to 2017, the overall improvement in ecological vulnerability in the whole TRB showed that the areas with great ecological improvement increased by 46.11%, while the areas with ecological degradation decreased by 9.64%. The vegetation cover and potential evapotranspiration (PET) were the obvious driving factors, explaining 57.56% and 21.55% of the changes in ecological vulnerability across the TRB, respectively. In terms of ecological vulnerability grade changes, obvious spatial differences were observed in the upper, middle, and lower reaches of the TRB due to the different vegetation and hydrothermal conditions. The alpine source region of the TRB showed obvious ecological improvement due to increased precipitation and temperature, but the alpine meadow of the Kaidu River catchment in the Middle Tianshan Mountains experienced degradation associated with overgrazing and local drought. The improved agricultural management technologies had positive effects on farmland ecological improvement, while the desert vegetation in oasis-desert ecotones showed a decreasing trend as a result of cropland reclamation and intensive drought. The desert riparian vegetation in the lower reaches of the Tarim River was greatly improved due to the implementation of the EWDP, which has been active for tens of years. These results provide comprehensive knowledge about ecological processes and mechanisms in the whole TRB and help to develop environmental restoration measures based on different ecological vulnerability grades in each sub-catchment.

Snow cover is an important water source for vegetation growth in arid and semi-arid areas, and grassland phenology provides valuable information on the response of terrestrial ecosystems to climate change. The Mongolian Plateau features both abundant snow cover resources and typical grassland ecosystems. In recent years, with the intensification of global climate change, the snow cover on the Mongolian Plateau has changed correspondingly, with resulting effects on vegetation growth. In this study, using MOD10A1 snow cover data and MOD13A1 Normalized Difference Vegetation Index (NDVI) data combined with remote sensing (RS) and geographic information system (GIS) techniques, we analyzed the spatiotemporal changes in snow cover and grassland phenology on the Mongolian Plateau from 2001 to 2018. The correlation analysis and grey relation analysis were used to determine the influence of snow cover parameters (snow cover fraction (SCF), snow cover duration (SCD), snow cover onset date (SCOD), and snow cover end date (SCED)) on different types of grassland vegetation. The results showed wide snow cover areas, an early start time, a late end time, and a long duration of snow cover over the northern Mongolian Plateau. Additionally, a late start, an early end, and a short duration were observed for grassland phenology, but the southern area showed the opposite trend. The SCF decreased at an annual rate of 0.33%. The SCD was shortened at an annual rate of 0.57 d. The SCOD and SCED in more than half of the study area advanced at annual rates of 5.33 and 5.74 DOY (day of year), respectively. For grassland phenology, the start of the growing season (SOS) advanced at an annual rate of 0.03 DOY, the end of the growing season (EOS) was delayed at an annual rate of 0.14 DOY, and the length of the growing season (LOS) was prolonged at an annual rate of 0.17 d. The SCF, SCD, and SCED in the snow season were significantly positively correlated with the SOS and negatively correlated with the EOS and LOS. The SCOD was significantly negatively correlated with the SOS and positively correlated with the EOS and LOS. The SCD and SCF can directly affect the SOS of grassland vegetation, while the EOS and LOS were obviously influenced by the SCOD and SCED. This study provides a scientific basis for exploring the response trends of alpine vegetation to global climate change.

The purpose of the current study was to investigate the eco-physiological responses, in terms of growth and C:N:P stoichiometry of plants cultured from dimorphic seeds of a single-cell C₄ annual Suaeda aralocaspica (Bunge) Freitag and Schütze under elevated CO₂. A climatic chamber experiment was conducted to examine the effects of ambient (720 μg/L) and CO₂-enriched (1440 μg/L) treatments on these responses in S. aralocaspica at vegetative and reproductive stages in 2012. Result showed that elevated CO₂ significantly increased shoot dry weight, but decreased N:P ratio at both growth stages. Plants grown from dimorphic seeds did not exhibit significant differences in growth and C:N:P stoichiometric characteristics. The transition from vegetation to reproductive stage significantly increased shoot:root ratio, N and P contents, but decreased C:N, C:P and N:P ratios, and did not affect shoot dry weight. Moreover, our results indicate that the changes in N:P and C:N ratios between ambient and elevated CO₂ are mainly caused by the decrease of N content under elevated CO₂. These results provide an insight into nutritional metabolism of single-cell C₄ plants under climate change.

There are numerous valley farmlands on the Chinese Loess Plateau (CLP), where suffers from low soil quality and high risk of soil salinization due to the shallow groundwater table and poor drainage system. Currently, research on the evolution processes and mechanisms of soil quality and salinization in these dammed-valley farmlands on the CLP is still inadequately understood. In this study, three kinds of dammed-valley farmlands in the hilly-gully areas of the northern CLP were selected, and the status of soil quality and the impact factors of soil salinization were examined. The dammed-valley farmlands include the new farmland created by the project of Gully Land Consolidation, the 60-a farmland created by sedimentation from check dam, and the 400-a farmland created by sedimentation from an ancient landslide-dammed lake. Results showed that (1) the newly created farmland had the lowest soil quality in terms of soil bulk density, porosity, soil organic carbon and total nitrogen among the three kinds of dammed-valley farmlands; (2) soil salinization occurred in the middle and upper reaches of the new and 60-a valley farmlands, whereas no soil salinization was found in the 400-a valley farmland; and (3) soil salinization and low soil nutrient were determined to be the two important factors that impacted the soil quality of the valley farmlands in the hilly-gully mountain areas of the CLP. We conclude that the dammed-valley farmlands on the CLP have a high risk of soil salinization due to the shallow groundwater table, alkalinity of the loessial soil and local landform feature, thus resulting in the low soil quality of the valley farmlands. Therefore, strengthening drainage and decreasing groundwater table are extremely important to improve the soil quality of the valley farmlands and guarantee the sustainable development of the valley agriculture on the CLP.

Studies on the ecosystem service value (ESV) of gardens are critical for informing evidence- based land management practices based on an understanding of the local ecosystem. By analyzing equivalent value factors (EVFs), this paper evaluated the values of 11 ecosystem services of gardens in the Yellow River Basin of China in 2019. High-precision land use survey data were used to improve the accuracy of the land use classification, garden areas, and spatial distribution of the ESVs of gardens. The results showed that garden ecosystem generally had high ESVs, especially in terms of the ESV of food production, which is worthy of further research and application to the practice of land use planning and management. Specifically, the value of one standard EVF of ecosystem services in 2019 was 3587.04 CNY/(hm²•a), and the ESV of food production of gardens was much higher than that of croplands. Garden ecosystem provided an ESV of 1348.66×10⁸ CNY/a in the Yellow River Basin. The areas with the most concentrated ESVs of gardens were located in four regions: downstream in the Shandong-Henan zone along the Yellow River, mid-stream in the Shanxi-Shaanxi zone along the Yellow River, the Weihe River Basin, and upstream in the Qinghai-Gansu-Ningxia-Inner Mongolia zone along the Yellow River. The spatial correlation of the ESVs in the basin was significant (global spatial autocorrelation index Moran's I=0.464), which implied that the characteristics of high ESVs adjacent to high ESVs and low ESVs adjacent to low ESVs are prominent. In the Yellow River Basin, the contribution of the ESVs of gardens to the local environment and economy varied across regions. We also put forward some suggestions for promoting the construction of ecological civilization in the Yellow River Basin. The findings of this study provide important contributions to the research of ecosystem service evaluation in the Yellow River Basin.

Coal mining has led to serious ecological damages in arid desert region of Northwest China. However, effects of climatic factor and mining activity on vegetation dynamics and plant diversity in this region remain unknown. Wuhai City located in the arid desert region of Northwest China is an industrial city and dominated by coal mining. Based on Landsat data and field investigation in Wuhai City, we analyzed the vegetation dynamics and the relationships with climate factors, coal mining activity and ecological restoration projects from 2000 to 2019. Results showed that vegetation in Wuhai City mostly consisted of desert plants, such as Caragana microphylla, Tetraena mongolica and Achnatherum splendens. And the vegetation fractional coverage (VFC) and greenness rate of change (GRC) showed that vegetation was slightly improved during the study period. Normalized difference vegetation index (NDVI) was positively correlated with annual mean precipitation, relative humidity and annual mean temperature, indicating that these climate factors might play important roles in the improved vegetation. Vegetation coverage and plant diversity around the coal mining area were reduced by coal mining, while the implementation of ecological restoration projects improved the vegetation coverage and plant diversity. Our results suggested that vegetation in the arid desert region was mainly affected by climate factors, and the implementation of ecological restoration projects could mitigate the impacts of coal mining on vegetation and ecological environment.

Nitrogen (N) and phosphorus (P) are two essential nutrients that determine plant growth and many nutrient cycling processes. Increasing N and P deposition is an important driver of ecosystem changes. However, in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands, how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood. Therefore, we conducted an N and P addition experiment (involving control, N addition, P addition, and N+P addition) in an alpine grassland on Kunlun Mountains (Xinjiang Uygur Autonomous Region, China) in 2016 and 2017 to investigate the changes in leaf nutrient concentrations (i.e., leaf N, Leaf P, and leaf N:P ratio) and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata, which are dominant species in this grassland. Results showed that N addition has significant effects on soil inorganic N (NO₃^--N and NH₄⁺-N) and leaf N of both species in the study periods. Compared with green leaves, leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S. rhodanthum was more sensitive to N addition, whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S. capillata. N addition did not influence N resorption efficiency of the two species. P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period. These influences on plants can be explained by increasing P availability. The present results illustrated that the two species are more sensitive to P addition than N addition, which implies that P is the major limiting factor in the studied alpine grassland ecosystem. In addition, an interactive effect of N+P addition was only discernable with respect to soil availability, but did not affect plants. Therefore, exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.

With realizing the importance of ecosystem services to society, the efforts to evaluate the ecosystem services have increased. As the largest tributary of the Yellow River, the Weihe River has been endowed with many ecological service functions. Among which, water yield can be a measure of local availability of water and an index for evaluating the conservation function of the region. This study aimed to explore the temporal and spatial variation of water yield and its influencing factors in the Weihe River Basin (WRB), and provide basis for formulating reasonable water resources utilization schemes. Based on the InVEST (integrated valuation of ecosystem services and tradeoffs) model, this study simulated the water yield in the WRB from 1985 to 2019, and discussed the impacts of climatic factors and land use change on water yield by spatial autocorrelation analysis and scenario analysis methods. The results showed that there was a slight increasing trend in water yield in the WRB over the study period with the increasing rate of 4.84 mm/10a and an average depth of 83.14 mm. The main water-producing areas were concentrated along the mainstream of the Weihe River and in the southern basin. Changes in water yield were comprehensively affected by climate and underlying surface factors. Precipitation was the main factor affecting water yield, which was consistent with water yield in time. And there existed significant spatial agglomeration between water yield and precipitation. Land use had little impact on the amount of water yield, but had an impact on its spatial distribution. Water yield was higher in areas with wide distribution of construction land and grassland. Water yield of different land use types were different. Unused land showed the largest water yield capacity, whereas grassland and farmland contributed most to the total water yield. The increasing water yield in the basin indicates an enhanced water supply service function of the ecosystem. These results are of great significance to the water resources management of the WRB.

Nitraria tangutorum nebkhas are widely distributed in the arid and semi-arid desert areas of China. The formation and development of N. tangutorum nebkhas are the result of the interaction between vegetation and the surrounding environment in the process of community succession. Different successional stages of N. tangutorum nebkhas result in differences in the community structure and composition, thereby strongly affecting the distribution of soil nutrients and ecosystem stability. However, the ecological stoichiometry of N. tangutorum nebkhas in different successional stages remains poorly understood. Understanding the stoichiometric homeostasis of N. tangutorum could provide insights into its adaptability to the arid and semi-arid desert environments. Therefore, we analyzed the stoichiometric characteristics of N. tangutorum in four successional stages, i.e., rudimental, developing, stabilizing, and degrading stages using a homeostasis model in an oasis-desert ecotone of Northwest China. The results showed that soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents and their ratios in the 0-100 cm soil depth were significantly lower than the averages at regional and global scales and were weakly influenced by successional stages in the oasis-desert ecotone. TN and TP contents and C:N:P in the soil showed similar trends. Total carbon (TC) and TN contents in leaves were 450.69-481.07 and 19.72-29.35 g/kg, respectively, indicating that leaves of N. tangutorum shrubs had a high storage capacity for C and N. Leaf TC and TN contents and N:P ratio increased from the rudimental stage to the stabilizing stage and then decreased in the degrading stage, while the reverse trend was found for leaf C:N. Leaf TP content decreased from the rudimental stage to the degrading stage and changed significantly in late successional stages. N:P ratio was above the theoretical limit of 14, indicating that the growth of N. tangutorum shrubs was limited by P during successional stages. Leaf N, P, and N:P homeostasis in four successional stages was identified as ''strictly homeostasis''. Redundancy analysis (RDA) revealed that soil acidity (pH) and the maximum water holding capacity were the main factors affecting C:N:P stoichiometric characteristics in N. tangutorum leaves. Our study demonstrated that N. tangutorum with a high degree of stoichiometric homeostasis could better cope with the arid desert environment.

Mounds constructed by plateau zokors, which is widely distributed in alpine meadows significantly modified plant community structure. However, the variations of plant community structure under the disturbance of plateau zokor-made mound are less concerned. Therefore, we investigated the responses of plant community on zokor-made mound of different years (1 a and 3-4 a), and compared with undisturbed sites (no mound) in an alpine meadow in the eastern Qinghai-Tibetan Plateau (QTP), China. Species richness, coverage and Simpson diversity index were all significantly reduced by the presence of zokor-made mound, but plant heights were significantly increased, particularly in grasses and sedges. Several perennial forage species showed an increased importance value and niche breadth, including Koeleria macrantha, Elymus nutans and Poa pratensis. The effect of zokor-made mound on niche overlap showed that more intense interspecific competition produced a greater utilization of environmental resources. And this interspecific niche overlap was strengthened as succession progressed. The bare mound created by zokor burrowing activities provided a colonizing opportunity for non-dominant forage species, resulting in abundant plant species and plant diversity during the succession period. We concluded that presence of zokor-made mound was conducive to regeneration and vitality of plant community in alpine meadows, thus improving their resilience to anthropogenic stress.

The distribution of binding agents (i.e., soil organic carbon (SOC) and glomalin-related soil protein (GRSP)) in soil aggregates was influenced by many factors, such as plant characteristics and soil properties. However, how these factors affect binding agents and soil aggregate stability along a climatic gradient remained unclear. We selected the Robinia pseudoacacia L. forests from semi-arid to semi-humid of the Loess Plateau, China to analyze the plant biomass, soil physical-chemical properties, SOC and GRSP distribution in different sized soil aggregates. We found that from semi-arid to semi-humid forests: (1) the proportion of macro-aggregates (>0.250 mm) significantly increased (P<0.05), whereas those of micro-aggregates (0.250-0.053 mm) and fine materials (<0.053 mm) decreased and soil aggregate stability was increased; (2) the contents of SOC and GRSP in macro-aggregates and micro-aggregates significantly increased, and those in fine materials decreased; (3) the contribution of SOC to soil aggregate stability was greater than those of total GRSP and easily extractable GRSP; (4) soil properties had greater influence on binding agents than plant biomass; and (5) soil aggregate stability was enhanced by increasing the contents of SOC and GRSP in macro-aggregates and soil property was the important part during this process. Climate change from semi-arid to semi-humid forests is important factor for soil structure formation because of its positive effect on soil aggregates.

The water resources of the Nadhour-Sisseb-El Alem Basin in Tunisia exhibit semi-arid and arid climatic conditions. This induces an excessive pumping of groundwater, which creates drops in water level ranging about 1-2 m/a. Indeed, these unfavorable conditions require interventions to rationalize integrated management in decision making. The aim of this study is to determine a water recharge index (WRI), delineate the potential groundwater recharge area and estimate the potential groundwater recharge rate based on the integration of statistical models resulted from remote sensing imagery, GIS digital data (e.g., lithology, soil, runoff), measured artificial recharge data, fuzzy set theory and multi-criteria decision making (MCDM) using the analytical hierarchy process (AHP). Eight factors affecting potential groundwater recharge were determined, namely lithology, soil, slope, topography, land cover/use, runoff, drainage and lineaments. The WRI is between 1.2 and 3.1, which is classified into five classes as poor, weak, moderate, good and very good sites of potential groundwater recharge area. The very good and good classes occupied respectively 27% and 44% of the study area. The potential groundwater recharge rate was 43% of total precipitation. According to the results of the study, river beds are favorable sites for groundwater recharge.

Endophytic bacteria from halophytes have a wide range of application prospects in various fields, such as plant growth-promoting, biocontrol activity and stress resistance. The current study aimed to identify cultivable endophytic bacteria associated with halophytes grown in the salt-affected soil in Xinjiang Uygur Autonomous Region, China and to evaluate their plant beneficial traits and enzyme-producing activity. Endophytic bacteria were isolated from Reaumuria soongorica (PalL Maxim.), Artemisia carvifolia (Buch.-Ham. ex Roxb. Hort. Beng.), Peganum harmala L. and Suaeda dendroides (C. A. Mey. Moq.) by using the cultural-dependent method. Then we classified these bacteria based on the difference between their sequences of 16S rRNA (16S ribosomal RNA) gene. Results showed that the isolated bacteria from R. soongorica belonged to the genera Brucella, Bacillus and Variovorax. The bacteria from A. carvifolia belonged to the genera Micromonospora and Brucella. The bacteria from P. harmala belonged to the genera Paramesorhizobium, Bacillus and Peribacillus. The bacteria from S. dendroides belonged to the genus Bacillus. Notably, the genus Bacillus was detected in the three above plants, indicating that Bacillus is a common taxon of endophytic bacteria in halophytes. And, our results found that about 37.50% of the tested strains showed strong protease-producing activity, 6.25% of the tested strains showed strong cellulase-producing activity and 12.50% of the tested strains showed moderate lipase-producing activity. Besides, all isolated strains were positive for IAA (3-Indoleacetic acid) production, 31.25% of isolated strains exhibited a moderate phosphate solubilization activity and 50.00% of isolated strains exhibited a weak siderophore production activity. Our findings suggest that halophytes are valuable resources for identifying microbes with the ability to increase host plant growth and health in salt-affected soils.

Underlying terrain strongly influences dune formation. However, the impacts of underlying terrain on the dune formation are poorly studied. In the present research, we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin, Northwest China. We quantified the dunes' sediment characteristics on different types of underlying terrain and the terrain's effects on the surface quartz grains by analyzing grain-size distribution, soluble salt contents and grain surface micro-textures. Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution, whose peak corresponded to the saltation load. Linear dunes were mainly composed of fine sands with a bimodal frequency distribution, whose main peak represented the saltation load, and whose secondary peak represented the modified saltation or suspension load. Sand was transported from source area by running water (inland rivers) over short distances and by wind over relatively longer distances. Thus, quartz grains had poor roundness and were dominated by sub-angular and angular shapes. Surface micro-textures indicated that dune sands were successively transported by exogenic agents (glaciation, fluviation and wind). Soluble salt contents were low in dunes that developed in the alluvial fans, which represented a low-energy chemical environment, so the grain surface micro-textures mainly resulted from mechanical erosion, with weak micro-textures formed by SiO₂ solution and precipitation. However, soluble salt contents were much higher in dunes that developed in the dry salt flats, which indicated a high-energy chemical environment. Therefore, in addition to micro-structures caused by mechanical erosion, micro-textures formed by SiO₂ solution and precipitation also well developed. Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin, China.

The ability of plants to safely retain seeds in the mother plant is an adaptive mechanism described in many desert plants. However, research about delayed seed dispersal species in the desert of the United Arab Emirates (UAE) is lacking. This study aims to identify these delayed seed dispersal species and assess the relationships of the presence of delayed seed dispersal with plant growth form, habit, spatial dispersal, antitelechoric mechanism, and seed release time. The relationships between the presence of delayed seed dispersal and the above studied traits were assessed by using the Pearson Chi-square test and Nonlinear Principal Components Analysis (NLPCA). Results showed that a total of 46 delayed seed dispersal species were recorded (15.0% of 307 studied species) and the highest incidence occurred in the Fabaceae family (17.4%). Delayed seed dispersal species were predominantly perennial plants (73.9%) with spatial restricted dispersal (67.4%), which released seed in the dry season (45.7%). The dominant groups of delayed seed dispersal species were persistent fruits species and synaptospermy (28.3%). All graminoids showed persistent lignified fruits, while prostrate annuals were basicarpic species with myxospermy. Sandy habitats had the highest number of delayed seed dispersal species (54.3%), whereas salt flats had the lowest (23.9%). In the desert of the UAE, delayed seed dispersal species spread seeds until the end of the dry and windy season, thus breaking seed dormancy at this time and ensuring seed germination in the next arrival of the rainy season. This morphological and ecological adaptation of delayed dispersal species is essential to the survival and sustainable development of vegetation in desert environments.

The quantification of carbon storage in vegetation biomass is a crucial factor in the estimation and mitigation of CO₂ emissions. Globally, arid and semi-arid regions are considered an important carbon sink. However, they have received limited attention and, therefore, it should be a priority to develop tools to quantify biomass at the local and regional scales. Individual plant variables, such as stem diameter and crown area, were reported to be good predictors of individual plant weight. Stand-level variables, such as plant cover and mean height, are also easy-to-measure estimators of above-ground biomass (AGB) in dry regions. In this study, we estimated the AGB in semi-arid woody vegetation in Northeast Patagonia, Argentina. We evaluated whether the AGB at the stand level can be estimated based on plant cover and to what extent the estimation accuracy can be improved by the inclusion of other field-measured structure variables. We also evaluated whether remote sensing technologies can be used to reliably estimate and map the regional mean biomass. For this purpose, we analyzed the relationships between field-measured woody vegetation structure variables and AGB as well as LANDSAT TM-derived variables. We obtained a model-based ratio estimate of regional mean AGB and its standard error. Total plant cover allowed us to obtain a reliable estimation of local AGB, and no better fit was attained by the inclusion of other structure variables. The stand-level plant cover ranged between 18.7% and 95.2% and AGB between about 2.0 and 70.8 Mg/hm². AGB based on total plant cover was well estimated from LANDSAT TM bands 2 and 3, which facilitated a model-based ratio estimate of the regional mean AGB (approximately 12.0 Mg/hm²) and its sampling error (about 30.0%). The mean AGB of woody vegetation can greatly contribute to carbon storage in semi-arid lands. Thus, plant cover estimation by remote sensing images could be used to obtain regional estimates and map biomass, as well as to assess and monitor the impact of land-use change on the carbon balance, for arid and semi-arid regions.

Precipitation is one of the most important indicators of climate data, but there are many errors in precipitation measurements due to the influence of climatic conditions, especially those of solid precipitation in alpine mountains and at high latitude areas. The measured amount of precipitation in those areas is frequently less than the actual amount of precipitation. To understand the impact of climatic conditions on precipitation measurements in the mountainous areas of Northwest China and the applicability of different gauges in alpine mountains, we established a cryospheric hydrometeorology observation (CHOICE) system in 2008 in the Qilian Mountains, which consists of six automated observation stations located between 2960 and 4800 m a.s.l. Total Rain weighing Sensor (TRwS) gauges tested in the World Meteorological Organization-Solid Precipitation Intercomparison Experiment (WMO-SPICE) were used at observation stations with the CHOICE system. To study the influence of climatic conditions on different types of precipitation measured by the TRwS gauges, we conducted an intercomparison experiment of precipitation at Hulu-1 station that was one of the stations in the CHOICE system. Moreover, we tested the application of transfer functions recommended by the WMO-SPICE at this station using the measurement data from a TRwS gauge from August 2016 to December 2020 and computed new coefficients for the same transfer functions that were more appropriate for the dataset from Hulu-1 station. The new coefficients were used to correct the precipitation measurements of other stations in the CHOICE system. Results showed that the new parameters fitted to the local dataset had better correction results than the original parameters. The environmental conditions of Hulu-1 station were very different from those of observation stations that provided datasets to create the transfer functions. Thus, root-mean-square error (RMSE) of solid and mixed precipitation corrected by the original parameters increased significantly by the averages of 0.135 (353%) and 0.072 mm (111%), respectively. RMSE values of liquid, solid and mixed precipitation measurements corrected by the new parameters decreased by 6%, 20% and 13%, respectively. In addition, the new parameters were suitable for correcting precipitation at other five stations in the CHOICE system. The relative precipitation (RP) increment of different types of precipitation increased with rising altitude. The average RP increment value of snowfall at six stations was the highest, reaching 7%, while that of rainfall was the lowest, covering 3%. Our results confirmed that the new parameters could be used to correct precipitation measurements of the CHOICE system.